Development of a Hydrogen Microgas Turbine Combustor: NO_x Emissions and Secondary Air Injection

On the way to defossilization, green hydrogen is a promising way to substitute natural gas (NG) and oil in the gas turbine industry. In the scope of the H2mGT project, a microgas turbine (mGT) burner with $100%$ hydrogen firing is developed and validated. The project is funded by the German BMWK, and it is a collaboration between Technische Universität Berlin (TUB) and the manufacturer Euro-K GmbH. It consists of three phases: (1) atmospheric pressure tests with a fused silica combustion chamber; (2) atmospheric pressure tests with counterflow-cooled steel flame tube and secondary air injection; (3) validation of the burner in the mGT at elevated pressure levels. The current study will present the results of phase 2. The hydrogen burner used in the project is based on a swirl-stabilized burner of TUB and was scaled to 36 kW thermal power at atmospheric conditions. The burner design features a variable swirl intensity, additional axial momentum of air in the mixing tube, a movable central fuel lance, and pilot nozzles at the front plate. Furthermore, the steel flame tube is exchangeable, which allows the evaluation of different dilution hole patterns and, thus, the variation of the ratio of primary and secondary air. The study presents temperature, pressure, and emission measurements. It is found that the flame can be operated over a large range of equivalence ratios and preheating temperatures up to 500 °C. As expected, the NO_x emissions are mainly influenced by the local equivalence ratio, which can be controlled by the fuel mass flow or the dilution hole pattern in the flame tube. Furthermore, the results show a decrease of NO_x when the power density is increased at constant equivalence ratios, and a rise of NO_x during the fuel transition from natural gas to hydrogen. The results indicate certain differences to the findings of phase 1.